An OED is a device exhibiting various functions through exchange of charges between an electrode layer and an organic material, which includes an organic light emitting device (OLED), an organic solar cell, an organic photo conductor (OPC), and an organic transistor.
An OLED, which is a representative OED, conventionally includes a substrate, a first electrode layer, an organic layer including an emitting layer and a second electrode layer, which are sequentially stacked.
In the structure, which is, so called, a bottom emitting device, the first electrode layer may be a transparent electrode layer, and the second electrode layer may be a reflective electrode layer. In addition, in the structure, which is, so called, a top emitting device, the first electrode layer may be a reflective electrode layer, and the second electrode layer may be a transparent electrode layer.
Electrons and holes are injected respectively by the two electrode layers, and the injected electrons and holes are recombined in the emitting layer, resulting in generating light. The light may be emitted to the substrate in the bottom emitting device, and to the second electrode layer in the top emitting device.
In the structure of the OLED, indium tin oxide (ITO) generally used as the transparent electrode layer, the organic layer and the substrate, which is conventionally formed of glass, have refractive indexes of approximately 2.0, 1.8 and 1.5, respectively. In such a relationship of the refractive index, for example, the light generated in the organic emitting layer in the bottom emitting device is trapped at an interface between the organic layer and the first electrode layer or in the substrate due to a total internal reflection phenomenon, and only a very small amount of light is emitted.